The present invention relates to a body supporting furniture frame in which parallel cross-girders are secured between two opposite longitudinal girders, and at least the edges of the cross-girders are provided with a wire or a bar which is bent convexly upward in the longitudinal direction. One such body supporting furniture frame is disclosed in U.S. Pat. No. 3,842,452 of applicant. Generally speaking, when these wires or bars are loosely inserted in the corresponding lengthwise apertures of a cross-girder and when the wires and the corresponding lengthwise apertures have, for example, a circular cross-section, then, when such a cross-girder is subjected to a considerable load, the wires may deflect in the lengthwise apertures of the cross-girder, so that the latter adopts a concave shape. To obviate this disadvantage, U.S. Pat. No. 3,842,452 provides that these wires are rigidly joined in the cross-direction of the cross-girder in at least one place. Preferably these wires are rigidly joined substantially in the center of each cross-girder. The disadvantage of this design, however, is that in making such a body supporting furniture frame, whereby the wires of each cross-girder are rigidly joined, a number of additional components and additional procedures are necessary, so that the cost and price of the frame are adversely affected. It is an object of the present invention, therefore, to obviate this disadvantage.
The present invention is directed to a body supporting furniture frame having two opposite longitudinal girders and a plurality of mutually parallel cross-girders disposed therebetween, wherein at least the edges of the cross-girders are provided with a lengthwise aperture in which a wire or bar is loosely inserted, and the wires or bars are bent convexly upward in the longitudinal direction, and includes the improvement in accordance with which the cross-section of each lengthwise aperture and the cross-section of the corresponding wire or bar are designed with a mutually cooperating structural configuration such that the wire or bar is blocked in the lengthwise aperture against rotation through an angle exceeding 90.degree.. Preferably, the cross-section of each lengthwise aperture and the cross-section of the corresponding wire or bar are mutually adapted or designed so that the wire or bar may rotate in the lengthwise aperture through an angle between 0.degree. and 30.degree. only.
The present invention offers the advantage that, when such a cross-girder is subjected to a substantial load, the wires cannot deflect in the lengthwise apertures of the cross-girder. Another important advantage of the present invention is that it now becomes possible to manufacture such convexly upward bent cross-girders in a simple and inexpensive way. Thus, the plastic cross-girders can be made in a continuous manner or extruded in long sections by means of commercially available extrusion machines, after which the actual cross-girders can be sawed to the required length, for example, girders with a length of one meter. Subsequently, such a cross-girder with a suitable length is bent so that the curvature radius of the bent cross-girder is substantially equal to the curvature radius of two preliminarily bent wires or bars, so that as a result they can easily be slid into both lengthwise apertures of the cross-girder. Another advantage of the present invention is that in most embodiments the resisting moment to bending or the bending modulus I/V of the wires or bars is greater than the bending modulus I/V of wires with a circular cross-section. Since in each cross-girder these wires or bars are mainly subjected to bending, this means a better utilization of the reinforcing material.